Millimeter-Wave Tiny Lens Antenna Employing U-Shaped Filter Arrays for 5G

This letter presents a 28-GHz compact antenna array that employs a U-Shaped thin lens where a low-profile 1 × 4 antenna array is used as a feed source. The letter demonstrates that the proposed three-dimensional (3-D) U-Shaped lens designed by phase-shifting spatial filter arrays enables more than 3 dB peak gain enhancement even at the distance of less than half of the wavelength from the feed antenna. The first design step is to employ unit cells having a stable insertion loss and phase shift against the incident angle of electromagnetic waves without the gain degradation caused by undesired cavity effects, which is a critical bottleneck at such a short distance. In addition to this, the total gain is further enhanced by creating a novel 3-D U-Shaped architecture, enabling an increase in the effective aperture size because the U-Shaped thin lens can capture the radiated fields over a broader range of incident angles compared to the prior flat lens, which is more effective at a closer distance. This letter demonstrates that the proposed approach can achieve higher than 3.8 dB enhancement in peak gain compared to the antenna without the U-Shaped lens when the phase offset (PO) is 0°. When the levels of the PO are 45°, 90°, and 135°, gain enhancements of 3.4, 3, and 2 dB are also achieved, respectively.